These idea may be too late, but I just jumped onto this thread:
1) After you add the backerboard, thinset, tile, grout, tower box etc to the lid, it had to get MUCH heavier then it was when you showed it propped up and open. How heavy is the lid to open and are you still using that notched 2x to hold it open? Is that enough....and...
2) In each picture where you showed the lid open it wasn't open all the way (ie the lid wasn't in a vertical position. I've found I want my lid to open the entire 90 degrees so it's straight up and I can get kegs in and out of the back positions very cleanly. If your lid only opens say 85 degrees (not all the way to vertical) this could be a problem for you. Especially homebrew kegs....you'll find it's best not to be moving them around too much after you've got them into place so your sediment stays consolidated on the bottom of the keg and doesn't cloud your beer. (generally speaking...hefs/wits...different story).
3) AWESOME work. You're a craftsman. You put that kind of care into brewing beer and you're going to make great beer![]()
The weight did increase but still very easy to lift. I have not had any problem at all with adding kegs. I have placed 7.5 kegs in without a problem but usually stay with 5 gallon kegs now and every so often the wife has me make 2.5 gallons of margs for parties. I still use the same 2x4 to keep it open and works like a charm.